Extended nip shoe for a nip in a papermaking machine

Abstract

An extended nip shoe for a press section in a papermaking machine distributes a compressive force to an inrunning compliant transport system advancing a web of paper. The shoe introduces and maintains a film of lubricant throughout the extended nip shoe-compliant transport system interface. Similarly, release of the compressive force is gradual to eliminate points of high unit loads on the compliant transport system and paper web.

What is claimed is: 
     
       1. In a papermaking machine using a compliant transport system to move a web of paper over a hydrodynamic ramp on a hydrostatic shoe, the hydrostatic shoe including: an open fluid reservoir;   means for pressurizing the fluid in the reservoir to exert a force against an opposing surface to form a nip between the opposing surface and the pressurized fluid; and   means for advancing the hydrostatic shoe to exert pressure on a compliant transport system passing between the hydrostatic shoe and the opposing surface with which the hydrostatic shoe forms a nip; the improvement comprises:   means for supplying lubricant to the interface of the hydrodynamic ramp and the compliant transport system; and   ramp means for gradually subjecting the compliant transport system to the pressure exerted by the hydrostatic shoe, the ramp means comprising:   an inrunning nip surface extending approximately 1.5° from a line substantially tangent to a load arc, defined by the hydrostatic shoe against the nip forming surface, through a vertex of a wedge formed when the compliant transport system simultaneously contacts the hydrostatic shoe and the opposing surface with which the hydrostatic shoe forms a nip;   an outrunning nip surface extended approximately 1.5° from a line substantially tangent to the load arc, resulting from the hydrostatic shoe against the nip forming surface, through a vertex of a wedge formed when the compliant transport system ceases to simultaneously contact the hydrostatic shoe and the opposing surface with which the hydrostatic shoe forms a nip; and   means for controllably distributing the release of the pressure exerted by the hydrostatic shoe on side edge portions of the compliant transport system.   
     
     
       2. The invention of claim 1, wherein the means for supplying lubricant to the interface of the hydrodynamic ramp and the compliant transport system comprises: an open reservoir of lubricant;   means for raising the lubricant to a level sufficient to contact the entire width of the compliant transport system;   means for retaining a substantial amount of the lubricant in the reservoir during contact of the compliant transport system with the lubricant;   means for catching excess lubricant carried by the compliant transport system; and   means for circulating caught lubricant to the reservoir.   
     
     
       3. The invention of claim 1, wherein said vertex of the wedge associated with the outrunning nip surface located on the hydrostatic shoe where the compliant transport system is compressed to a predetermined maximum between the hydrostatic shoe and the opposing surface with which the hydrostatic shoe forms a nip; and   said vertex of the wedge associated with the outrunning nip surface located on the hydrostatic shoe where the compliant transport system ceases to be compressed to a predetermined maximum between the hydrostatic shoe and the opposing surface with which the hydrostatic shoe forms a nip.   
     
     
       4. The invention of claim 1 or 3, wherein the inrunning nip surface is extended approximately 2-4 inches at said angle of approximately 1.5° from the line substantially tangent to the load arc. 
     
     
       5. The invention of claim 1 or 3, wherein the means for controllably distributing the release of the pressure exerted by the hydrostatic shoe on side edge portions of the compliant transport system comprises edge surfaces inclined away from a line parallel to the plane of the surface with which the hydrostatic shoe forms a nip. 
     
     
       6. The invention of claim 1, wherein the hydrostatic shoe is pivotal about a point offset from a central axis of rotation for the shoe.